--append
This causes rsync to update a file by appending data onto
the end of the file, which presumes that the data that
already exists on the receiving side is identical with
the start of the file on the sending side.

–append参数使文件续传时直接开始传输已有部分后面的部分，和–partial的区别待研究。

–inplace

--inplace
This option changes how rsync transfers a file when its
data needs to be updated: instead of the default method
of creating a new copy of the file and moving it into
place when it is com- plete, rsync instead writes the
updated data directly to the destination file.